In one known polariser, a ferrite rod is axially located within a waveguide along which received signals are transmitted. The ferrite rod is surrounded by a bobbin which holds it in position and also acts as a former around which a coil is wound. By controlling the electrical current through the coil, the plane of polarisation of incident energy on the rod can be adjusted and hence the propagation of energy along the waveguide controlled.
The present invention arose from an attempt to provide an improved polariser.